Process for detecting trace amounts of lead in unleaded gasoline

ABSTRACT

A PROCESS FOR THE CHROMOGENIC DETECTION OF TRACE AMOUNTS OF LEAD IN UNLEADED GASOLINE. THE PROCESS INVOLVES EXTRACTION OF LEAD THE GASOLINE PHASE FOLLOWED BY PRECIPITATION OF THE LEAD AND SUBSEQUENT DETECTION THEREOF BY MEANS OF A SUITABLE CHROMOGENIC REAGENT. THE PROCESS IS CAPABLE OF DETECTING THE PRESENCE OF LEAD IN QUANTITIES AS LOW AS ABOUT 0.1 MG. OF LEAD AS THE METAL.

United States Patent Oflice 3,806,319 Patented Apr. 23, 1974 3,806,319 PROCESS FOR DETECTING TRACE AMOUNTS OF LEAD IN UNLEADED GASOLINE Leo A. Fabbro, Cranbury, and Clarence S. Wentzel, Parlin, NJ., assignors to Cities Service Oil Company, Tulsa, Okla. No Drawing. Filed Sept. 26, 1972, Ser. No. 292,369 Int. Cl. G01n 33/22, 21/06 US. Cl. 23-230 R 8 Claims ABSTRACT OF THE DISCLOSURE A process for the chromogenic detection of trace amounts of lead in unleaded gasoline. The process involves extraction of lead from the gasoline phase followed by precipitation of the lead and subsequent detection thereof by means of a suitable chromogenic reagent. The process is capable of detecting the presence of lead in quantities as low as about 0.1 mg. of lead as the metal.

BACKGROUND OF THE INVENTION Lead alkyls such as tetraethyl lead and tetramethyl lead have long been used as octane improvers in gasoline. However, the use of lead alkyls in gasoline has a number of disadvantages. For example, during combustion the lead alkyls are converted to lead oxides and metallic lead which are materials that foul sparkplugs and form deposits within the engine. Moreover, not only are lead alkyls extremely toxic, but the exhausts of engines operated on leaded gasoline contain finely divided metallic lead and lead compounds such as the oxides which are themselves toxic. Recent concern about air pollution has resulted in the reduction or even the total elimination of lead alkyls from many blends of gasoline. However, the problem exists that unleaded gasoline may become contaminated with trace amounts of lead alkyls from, for example, storage tank bottoms and pipes within a blending plant. Hence, there exists a need for a method to detect trace amounts of lead in unleaded gasoline.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a process for the detection of trace amounts of lead in unleaded gasoline.

It is another object of this invention to provide a sensitive test for the detection of trace amounts of lead in small samples of unleaded gasoline.

Yet other objects will be apparent to those skilled in the art.

The foregoing objects are achieved in accordance with the practice of this invention. Broadly, this invention consists of a process for the detection of trace amounts of lead in unleaded gasoline comprising the steps:

(a) Mixing a sample of the gasoline to be tested with a solution of a halogen in an alcohol containing up to about 8 carbons;

(b) Mixing the resultant mixture with dilute aqueous nitric acid;

(c) Separating the aqueous phase from the gasoline p (d) Agitating said aqueous phase with sodium sulfite to form a precipitate of lead sulfite;

(e) Filtering the mixture to remove the precipitate;

(f) Adding to the precipitate a buffer solution having a pH of about 2.8; and

(g) Thereafter adding to said precipitate a solution of sodium rhodizonate.

Thus, by the practice of this invention, there is provided a fast, sensitive, and relatively simple method for determining the presence of trace amounts of lead in unleaded gasoline.

DETAILED DESCRIPTION The instant invention provides a process for the chromogenic detection of trace amounts of lead in an unleaded gasoline. The process involves extraction of lead from the gasoline phase followed by precipitation of the lead and subsequent detection thereof by means of a suitable chromogenic reagent. The process requires only small samples and is capable of detecting the presence of lead in quantities as low as about 0.1 mg. of lead expressed as the metal.

In its broadest sense, the process involves agitating a sample of the gasoline to be tested with an alcoholic solution of a halogen. The mixture is then agitated or shaken with a dilute aqueous nitric acid solution. The aqeous phase is then separated from the hydrocarbon phase and agitated with sodium sulfite until the sodium sulfite dissolves and reacts with lead ions in the aqueous phase to form a precipitate of lead sulfite. The mixture is then filtered to remove the precipitate and the precipitate is treated with an acidic buffer. Thereafter, the precipitate has added thereto a chromogenic reagent, i.e., sodium rhodizonate. If lead is present, a pink-red color will develop.

Since the foregoing procedure is suflficiently sensitive to detect the presence of lead in quantities as small as about 0.1 mg. of lead expressed as the metal, the size of the gasoline samples used will depend on the concentration of lead alkyl in the gasoline. While sample size is not critical to the practice of this invention, simple experimentation will allow one skilled in the art to determine the size of the sample that is used. Generally, gasoline samples about 5-7 0 ml. in volume may be used whlie sample sizes of about 10-50 ml. are more typical. The principal requirements are that, if lead be present, the sample be large enough to contain at least about 0.1 mg. of lead expressed as the metal and small enough to be conveniently handled.

In the first step of the process of this invention, the sample of gasoline to be tested is agitated or shaken with an alcoholic solution of a halogen. Preferred alcohols are alkanols containing up to about 8 carbons. The most preferred alkanol is l-octanol. While any halogen may be used, iodine is preferred. The function of the halogen, e.g., iodine, is to decompose the lead alkyl. An especially preferred solution of iodine in l-octanol is a solution containing 10- mg. of iodine per milliliter.

It has been found that the extractability of lead in the subsequent aqueous nitric acid treatment is enhanced if the alcoholic solution of halogen contains in addition a quaternary ammonium salt. The preferred quaternary ammonium salt is methyl tricaprylyl ammonium chloride. Therefore, when the lead alkyl concentration in gasoline is extremely low, it is advantageous to employ a preferred alcoholic halogen solution containing 10 mg. of iodine per milliliter of l-octanol solution which in addition contains methyl tricaprylyl ammonium chloride at a concentration of about 1% by weight of the total solution.

The volume ratio of gasoline to the alcoholic halogen solution is broadly from about 1:1 to about 3:1. The preferred ratio of gasoline to alcoholic halogen is about 2:1. The sample of gasoline and the alcoholic halogen solution are mixed or shaken for a period of about 2 minutes which is generally sufficient time for the halogen to decompose the lead alkyl.

After the lead alkyl in the gasoline has been decomposed by contact with the alcoholic halogen solution which optionally may contain a quaternary ammonium salt, the mixture is agitated with a dilute aqueous nitric acid solution. During agitation with the dilute aqueous nitric acid, lead ions are extracted from the organic phase to the aqueous phase. The length of the mixing period is not critical, but about 2 minutes is usually sufiicient. An average of about 72% of the lead is extracted into the aqueous phase in this amount of time.

The concentration of the dilute aqueous nitric acid is not critical, but a concentration of about 0.1 N has been found to be convenient. The amount of dilute aqueous nitric acid used to extract lead ions from the gasoline phase is not especially critical. However, when about -50 ml. samples of gasoline are treated with alcoholic halogen in an approximately 2:1 gasoline to alcoholic solution volume ratio, about -30 ml., and preferably about ml., of dilute aqueous nitric acid have been found to be suitable volumes.

After the gasoline-alcohol solution has been agitated with dilute aqueous nitric acid for a suitable period of time, the aqueous phase is separated from the organic phase. The aqueous phase is then brought into contact and agitated with sodium sulfite. The purpose of the sodium sulfite is primarily to reduce the acidity of the aqueous extract, to reduce residual iodine to iodide ion, and to precipitate lead ions from aqueous solution as lead sulfite. The amount of sodium sulfite employed will vary depending on the volume and the concentration of the dilute aqueous nitric acid solution as well as the amount of lead ions in the aqueous solution. However, in the case where about 20 ml. of about 0.1 N nitric acid are used to extract the lead from the organic phase, about 0.4 to about 0.6 gram, and preferably about 0.5 g., of sodium sulfite is used.

The dilute aqueous nitric acid solution is agitated with the sodium sulfite until the sodium sulfite dissolves and reacts with the lead ions in solution to cause formation of a precipitate of lead sulfite. The mixture is then filtered. In a preferred embodiment of this invention, the filter has a small area to favor maximum concentration of the small amount of precipitate obtained. The precipitate is advantageously left on the filter medium. It is preferred that the filter and precipitate then be dried.

To the precipitate, which is preferably dry and on the filter medium, is added a drop of a buffer solution having a pH of about 2.8. The buffer is allowed to permeate the precipitate and the filter. A preferred buffer having a pH of 2.79 is prepared by dissolving 1.5 g. of tartaric acid and 1.9 g. of sodium bitartrate in 100 ml. of water.

After addition of the buffer solution, about 1 to 3 drops of an approximately 0.1-0.2 weight percent solution of sodium rhodizonate is added to the precipitate. A pink-red color indicates the presence of lead and is due to the formation of lead rhodizonate.

The following specific example will serve to further illustrate this invention.

EXAMPLE Several samples of unleaded gasoline containing trace amounts of lead as the alkyl are subjected to the procedure of this invention to determine the presence or absence of lead. Various sized samples of each gasoline are used. Each sample is shaken for about 2 minutes with a solution of iodine in l-octanol having a concentration of 10 mg. of

iodine/ml. of solution. To each gasoline-alcohol solution are then added 20 ml. of 0.1 N aqueous nitric acid and the mixture is mixed by shaking for about 2 minutes. The aqueous phase is then separated from the organic phase and placed in a container containing 0.5 g. of sodium sulfite. The mixture is agitated to allow the sodium sulfite to dissolve and react with lead ions in solution to thereby form a precipitate of lead sulfite. The mixture is then filtered through a small filter and the precipitate dried on the filter. To the center of the dried precipitate on the filter is added 1 drop of a buffer solution having a pH of 2.79 which is prepared by dissolving 1.5 g. of tartaric acid and 1.9 g. of sodium bitartrate in ml. of water. Thereafter, 1 to 3 drops of an approximately 0.1 weight percent solution of sodium rhodizonate is added to the filter. The development of a pink-red color indicates a positive test for the presence of lead. The following table shows the amount of lead alkyl, expressed as metallic lead, that is present in the gasoline; the size gasoline sample used; the volume of the iodine in l-octanol solution employed; and the result of the chromogenic test for the presence of lead.

Volume Grams lead/ Volume of of It in 1- gal. oi gasoline, octsnol, Test gasoline ml. ml. result 0. 013 I50 25 Positive. 0. 013 40 20 Do. 0. 013 30 15 D0. 0. 016 40 20 Do. 0. 016 30 15 Do. 0. 016 20 10 D0. 0.022 40 20 Do. 0.022 20 10 Do. 0. 022 10 5 Do.

It is apparent from the data in the above table that the instant invention provides a procedure whereby small samples of gasoline containing trace amounts of lead alkyl can be readily and easily tested for the presence of lead. It is also apparent that the chromogenic test for the presence of lead, which is a step in the process of this invention, is sufficiently sensitive to detect the presence of as little as about 0.1 mg. of lead.

It will be understood that, while this invention has been illustrated by specific examples, it is not limited thereto, Accordingly, while iodine in l-octanol has been illustrated, it will be understood that halogens in alcoholic solution in general may be used. It will be further understood that, particularly in the case of very low concentrations of lead alkyl, a quaternary ammonium salt is advantageously present in the alcoholic halogen solution. Furthermore, times as well as quantities and concentrations of reactants may be varied within the limits disclosed herein.

Therefore, this invention provides a fast, sensitive, and relatively simple procedure for determining the presence of trace amounts of lead alkyls in unleaded gasoline.

We claim:

1. A process for the detection of trace amounts of lead in unleaded gasoline comprising the steps:

(a) mixing a sample of the gasoline to be tested with a solution of a halogen in an alcohol containing up to 8 carbons;

(b) mixing the resultant mixture with dilute aqueous nitric acid;

(c) separating the aqueous phase from the gasoline phase;

((1) agitating said aqueous phase with sodium sulfite to form a precipitate of lead sulfite;

(e) filtering the mixture to remove therefrom the precipitate;

(f) adding to the precipitate a buffer solution having a pH of about 2.8; and

(g) thereafter adding to said precipitate a solution of sodium rhodizonate.

2. The process of claim 1 wherein the solution of a halogen in an alcohol is a solution of iodine in l-octanol.

3. The process of claim 2 wherein the volume ratio of gasoline to the solution of iodine in l-octanol is about 2:1.

4. The process of claim 3 wherein the precipitate is allowed to dry on the filter before adding the buffer solution thereto.

5. The process of claim 4 wherein the solution of iodine in l-octanol has a concentration of about 10 mg. of iodine/ml. of solution.

6. The process of claim 5 wherein the buffer solution has a pH of 2.79 and is comprised of an aqueous solution of tartaric acid and sodium bitartrate having a composition corresponding to 1.5 g. of tartaric acid, 1.9 g. of sodium bitartrate, and 100 ml. of water.

7. The process of claim 6 wherein the dilute aqueous iodine in 1-octanol in addition contains 1% by weight of said solution of methyl tricaprylyl ammonium chloride.

References Cited Indust. and Eng. Chem., Anal. Ed., vol. 10, pp. 599- 600, 1938.

Indust. and Eng. Chem, Anal. Ed., vol. 13, p. 631, 1941.

Chem. Abs, 128496m, vol. 74, 1971.

MORRIS o. WOLK, Primary Examiner R. E. SERWIN, Assistant Examiner US. Cl. X.R.

nitric acid solution has a concentration of about 0.1 N. 15 23-230 M 8. The process of claim 7 wherein the solution of g;';g I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,806,319 Dated Apr. 23, I974 wfls) L A. Fabbro, and C. S. wentzeI It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below;

Column 4, I1'ne'6I after "to" the word about shouId be inserted. .1

Signed and sealed this 24th day of September 1974.

(SEAL) Attest:

C. MARSHALL DANN Commissioner of Patents McCOY M. GIBSON JR. Attesting Officer 

